1. Field of the Invention
The present invention relates to an optical glass fiber coating composition suitable for use as a primary coating on an optical glass fiber. More particularly this invention relates to an optical glass fiber coating composition which when coated on an optical glass fiber and suitably cured exhibits the combination of properties of low tensile modulus at room temperature, sufficient adhesion to the optical glass fiber to prevent structural defects and microbending in the optical glass fiber, and being strippable from the optical glass fiber while leaving substantially no residue on the optical glass fibers.
2. Description of Related Art
Optical glass fibers are typically provided with one or more coatings of a UV-curable coating composition that when suitably cured protect the optical glass fiber from begin damaged by attack from moisture or mechanical forces. The coating adjacent to the optical glass fiber is known as the primary coating. The primary coating must have a low tensile modulus at room temperature in order to prevent attenuation of the signal transmission caused by structural defects in the interface op the optical glass fibers and the resin, micro bending, and the like.
Because of the high integration of optical cables in recent years and the use of these cables in temperatures below room temperature, the primary coating must have a tensile modulus much lower than that of the primary coatings commonly used for the purpose of reducing attenuation of the signal transmission. Furthermore, to ensure use of the optical glass fibers under low temperature conditions with a minimal attenuation of the signal transmission, the primary coating must have a low and stable tensile modulus over a broad range of temperatures below room temperature.
To join optical glass fibers together or to other components, typically a portion of the coating material must be stripped from optical glass fiber. For this purpose, the primary coating must be strippable form the optical glass fiber while leaving substantially no residue on the optical glass fiber. The primary coating must also have adequate adhesion to the optical glass fiber to prevent structural defects, micro-bending, and the like.
There is a need for an optical glass fiber coating composition which when suitable cured exhibits a low tensile modulus at room temperature that is stable over a broad range of temperatures below room temperature, had adequate adhesion to the optical glass fiber to prevent structural defects, micro-bending, and the like, and yet is strippable from the optical glass fiber while leaving substantially no residue on the optical glass fiber. In WO-A-92/06846 and WO-A-93/21248 compositions are described having urethaneacrylate oligomers based on copolymers from at least ethylene oxide and butylene oxide. Although these optical fiber coating compositions exhibit useful properties, a further improvement is required.